Hand Movements May Send ADHD Signals

Action Points

Explain that measuring unintended hand movements in children with ADHD may help reveal the severity of the disorder.

Explain that in another study, short interval cortical inhibition was reduced in children with ADHD, but this lack of inhibition also correlated with greater severity of the disorder, suggesting that the motor cortex may be a marker for both the diagnosis and severity of ADHD.

Measuring unintended hand movements in children with attention deficit hyperactivity disorder (ADHD) may help reveal the severity of the disorder -- and ultimately may help shed light on its causes -- researchers predicted.

In a study that utilized a one-handed finger-tapping test and measured the excessive movements in the other hand, children with ADHD had twice as much of this "overflow" movement as normally developing children (P=0.01), Stewart H. Mostofsky, MD, of Johns Hopkins, and colleagues reported.

And in a second related study that assessed abnormal brain signaling in children with ADHD, the Mostofsky team found that children with ADHD had 40% (P<0.0001) less cortical inhibition than their typically developing counterparts.

Both studies were published in the Feb. 15 issue of Neurology.

"Together, these two studies provide support for the hypothesis that inhibition is an important mechanism in cognitive and behavioral function," Jonathan W. Mink, MD, PhD, of the University of Rochester in New York wrote in an editorial in the same issue.

David Rosenberg, MD, of Wayne State University in Detroit, described this work in an e-mail to MedPage Today and ABC News as "an important study" that "helps advance the field."

Previous studies of motor overflow in ADHD have provided only limited qualitative data.

To investigate more quantitative means of measurement, Mostofsky and colleagues enrolled 25 right-handed children with ADHD who ranged in age from 8 to 13 and 25 normal controls.

The children were asked to successively tap each finger to the thumb of the same hand in a fixed sequence.

Using a device known as a goniometer that measured hand movements in the opposite hand (mirror overflow), they were able to quantify both phasic overflow, which was defined as bidirectional finger movement, as well as total overflow, which referred to any change in finger position from baseline.

The investigators found that in boys with ADHD, but not girls, both phasic and total mirror overflow were greater than in controls (P=0.01 and P=0.02, respectively).

They also observed that phasic overflow in boys with ADHD occurred only during left-hand finger tapping (44.50 versus 11.60 in controls, P=0.006).

This finding may reflect the later motor development in the nondominant hand, according to the researchers.

In addition, the overflow scores during right-hand finger tapping correlated with hyperactivity and impulsivity scores as rated by parents (R=0.51, P=0.04).

"The finding in boys rather than girls is of interest and worth further investigation," wrote Rosenberg, who was not involved in the study.

"Even more important would be determining whether this finding is specific to ADHD or seen in other psychiatric disorders," he added.

In discussing their findings, the investigators explained, "Mirror overflow is thought to result from impaired inhibition of involuntary synkinetic movements. Impairment of voluntary response inhibition has been hypothesized to contribute to the core diagnostic features of excessive hyperactivity, impulsivity, and off-task behavior."

A limitation of this study, they acknowledged, was the lack of data on movement amplitude, which they hope to investigate in the future.

In the second study, which assessed short interval cortical inhibition through transcranial magnetic stimulation, Mostofsky's group found that not only was short interval cortical inhibition reduced in children with ADHD, but this lack of inhibition also correlated with greater severity of the disorder (R=−0.52, P=0.002).

This study included 49 children with ADHD, whose mean age was 11, and 49 matched controls.

The children's developmental skills also were rated, on the Physical and Neurological Examination for Subtle Signs (PANESS) scale.

These factors also accounted for variance in severity of symptoms as measured on the ADHD rating scale:

PANESS, 26.3%

Short interval cortical inhibition, 13.3%

Cortical silent periods, 6.7%

However, in a final linear regression model, only short interval cortical inhibition accounted for the severity of ADHD symptoms (R2=0.24, P=0.0045).

The investigators also found no evidence that the link between cortical inhibition and ADHD was influenced by the use of stimulant medications.

"Our results suggest that motor cortex [short interval cortical inhibition] is a quantitative, biologically based marker of both the categorical diagnosis of ADHD and the severity of ADHD symptoms in children at an age during which rapid motor and physiologic development is occurring," Mostofsky and colleagues stated.

The study was limited by its cross-sectional design, but refinements in the transcranial coil stimulator will most likely be needed before a longitudinal study can be done, they noted.

Michael J. Manos, PhD, of the Cleveland Clinic, described the findings of these studies in an e-mail message to MedPage Today and ABC News as "quite valuable."

"The results may lead to new methods of diagnosing ADHD in children. Even more important is the possibility that the methods, once developed, would assist us in monitoring response to the medical treatment of ADHD," wrote Manos, who was not involved in the work.

This article was developed in collaboration with ABC News.

Several of the investigators report receiving research support from the National Institutes of Health, as well as other organizations including the Tourette Syndrome Association, the American Academy of Neurology, and the Cincinnati Children's Hospital Research Foundation.

One author also receives royalties from publication of Rapid Automatized Naming and Rapid Alternating Stimulus Tests, and the lead investigator has acted as scientific adviser for Bristol-Myers Squibb.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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